(1) Field of the Invention
The invention relates to a series of retardants, and more particularly to a polymerization retardant of aniline and a chemical composition for polyaniline preparation.
(2) Description of the Prior Art
The first conducting polymer was synthesized in 1862, Letherbyl observed the green-blue deposition grown on the platinum electrode by electrolysis of aniline solution. It was named “Aniline black” because it was uncharacterized at that time. In 1986, the conductivity of polyaniline had been increased from 10−11 S/cm to 10 S/cm by chemical oxidation of aniline in the presence of protic acid. In 1994, MacDiarmid addressed that the conductivity of polyaniline can be brought up to 200 S/cm by using camphorsulfonic acid (CSA) as dopant. The remarkable conductivity of polyaniline makes it more applicable.
Aniline is colorless liquid with boiling point of 184° C. and density of 1.022 g/cm3. It can be polymerized by either electrochemical method or chemical oxidation to produce polyaniline. Polyaniline possesses several nice properties, such as high conductivity, high stability, low cost, simple synthesis process, and structure variety. Those characteristics make polyaniline widely applicable and also the very first commercialized conducting polymer.
Although polyaniline carries such advantages, however, low solubility in solvents make it difficult to do further processing, for example, coating. To avoid that, polyaniline was usually polymerized in situ by applying the solution of aniline monomer and oxidant on the substrate and process polymerization on it directly. In general, aniline monomer would be polymerized rapidly (in few minutes) once mixed with oxidant. While polymerization occurred, polyaniline precipitated from solvent and dramatically increase the viscosity of solution. That means the operating time was limited, solution of aniline monomer and oxidant should be used on substrate in few minutes or it will spoiled. The rapid polymerization rate of aniline is a major problem in many fields, such as in electrolytic capacitor, the most successful application of conducting polymer. The electrode of electrolytic capacitors is a highly porous substrate. The pore size is about 50 nm˜2 μm. Conducting polymer was coated on the porous substrate to form a electrolytic capacitor. FIG. 1A˜FIG. 1B is showing micro structure of the cross section of capacitor electrode 1. Conducting polymer 2 was coated into the micro pore 11. In the case of too fast polymerization, the viscosity of monomer solution increased rapidly that cause the incomplete coating of conducting polymer 2 and leave vacancy 111. These vacancy 111 would damage the capacitor by lower capacity, lower reliability, and increase the equivalent series resistance (ESR).
Therefore, controlling the aniline polymerization rate is one of the most important points for bringing polyaniline to extensive application.